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pam_ssh - authentication and session management with SSH private keys


SSH Authentication Module
SSH Session Management Module
See Also


[service-name] module-type control-flag pam_ssh [options]


The SSH authentication service module for PAM, pam_ssh provides functionality for two PAM categories: authentication and session management. In terms of the module-type parameter, they are the "auth" and "session" features.

SSH Authentication Module

The SSH authentication component provides a function to verify the identity of a user (pam_sm_authenticate), by prompting the user for a passphrase and verifying that it can decrypt the target user’s SSH key using that passphrase.

The following options may be passed to the authentication module:

use_first_pass If the authentication module is not the first in the stack, and a previous module obtained the user’s password, that password is used to authenticate the user. If this fails, the authentication module returns failure without prompting the user for a password. This option has no effect if the authentication module is the first in the stack, or if no previous modules obtained the user’s password.
try_first_pass This option is similar to the use_first_pass option, except that if the previously obtained password fails, the user is prompted for another password.
nullok Normally, keys with no passphrase are ignored for authentication purposes. If this option is set, keys with no passphrase will be taken into consideration, allowing the user to log in with a blank password.

SSH Session Management Module

The SSH session management component provides functions to initiate (pam_sm_open_session) and terminate (pam_sm_close_session) sessions. The pam_sm_open_session function starts an SSH agent, passing it any private keys it decrypted during the authentication phase, and sets the environment variables the agent specifies. The pam_sm_close_session function kills the previously started SSH agent by sending it a SIGTERM.

The following options may be passed to the session management module:

want_agent Start an agent even if no keys were decrypted during the authentication phase.


$HOME/.ssh/identity SSH1 RSA key
$HOME/.ssh/id_rsa SSH2 RSA key
$HOME/.ssh/id_dsa SSH2 DSA key


ssh-agent(1), pam.conf(5), pam(8)


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